Tubes are used in many medical and non-medical applications. For example, tracheostomy tube assemblies commonly include an outer tube and an inner tube or cannula that is a removable fit within the outer tube. The inner tube can be removed and replaced periodically to ensure that the passage through the assembly does not become blocked by secretions. This avoids the need frequently to remove the outer tube.
The inner tube presents various problems because it must be thin walled and a close fit within the outer tube so as to limit the resistance to flow of gas along the assembly. It must, however, also be sufficiently stiff to be inserted in the outer tube without buckling or kinking. A particularly suitable material for the inner cannula is PTFE or expanded PTFE (ePTFE). The use of such a material in an inner cannula is described in WO94/01156 and in WO2004/101048. The Flextra tube sold by Tyco Healthcare is made of ePTFE. Whilst such a material has various advantages, the material makes it difficult to attach a hub or end fitting to the machine end of the shaft of the cannula securely in a reliable and low cost manner. There are also other tubes where it can be difficult to attach an end fitting.
It is an object of the present invention to provide an alternative tube and a method of its manufacture.